A stator of an electric motor and the like is locked to a casing, for example, by arranging a plurality of unit cores corresponding to teeth, which are coil winding object, along a periphery and inserting a key into a key hole constituted by a key groove formed in an outer circumference of a single specific unit core and a key groove formed in the casing.
In the unit core, teeth are formed in the inner circumference, and a yoke is formed in the outer circumference. In addition, the key groove is further formed in the outer circumference of the specific unit core.
As the key is inserted into the key hole, a plurality of unit cores are locked to the casing in a contracted state by virtue of a so-called interference fit, so that the stator core is integrated with the casing.
In this state, the key prevents a relative displacement between the stator core and the casing in a rotation direction.
It is necessary to prevent the key from falling off the key groove. For this purpose, JU H05-015647 A, published by the Japan Patent Office in 1993, proposes a method of press-fitting a tapered pin into the key hole.